No airflow from floor vents air goes to defrost instead.

I have a 1997 F150. The problem I am having is when I turn the selector switch to floor or floor/panel etc., the air comes out of the defrost vents instead of the floor. Everything else when I turn the switch works fine (panel, defrost etc.). Can someone please give me an idea of what may have happened so I can fix this problem.

I have the exact same problem with my '97 and just logged on to post something. I believe this is probably related to a leaking vacuum line connected to the function selector switch, or perhaps the switch itself is bad. I just discovered this on mine the other day. In addition, when I select "Floor/Panel", the compressor engages, which I don't think it's supposed to do. I'll probably wind up taking mine to the dealer since I don't have time to shade tree this problem. If you find an easy cure please post something.

when there is a problem with the system vacuum, the hvac unit defaults to defrost.

Your vacuum hoses are up and to the right of the gas pedal. Check for loose connections there and listen for hissing (to indicate a leak)

---- the A/C clutch ----
Your A/C clutch engages in all positions except for vent and floor.
Why?:
(1) a/c and max a/c: reason given
(2) "vent" with a/c is the "a/c" selector
(3) floor: floor is mainly used for heat. Also, cold air travels down.
(4) floor+panel: a/c comes on because it is requested by a majority of the people (hot body and hot feet are a thing of the past)
(5) floor+defrost and defrost: anytime the defrost vent has air blowing out the a/c is on as a safety measure against fogging.

Ok, I took my truck into the dealer, and they fixed the problem. Apparently, the lever to the vacuum motor came off or disconnected somehow. They put it back on. Total cost: $116.35. I hope this saves you some money. Good Luck.

I had the same problem with my '97. As I recall (it was over a year ago I that fixed it) the vacuum motor is behind the floor air duct and slightly to the left. I reconnected the linkage and about two days later the same problem happened again. After removing the vacuum motor I noticed that when I switched it to the floor position the diaphragm in the vacuum motor pulled in on one side sooner than the other. This caused the linkage to slip out of the hole in the door that directs the air. The linkage was too stiff to bend so I rotated the vacuum motor 180 degrees so that when the diaphragm pulls in unevenly it tends to push the linkage farther into the hole in the air door rather than pull it out of it. The only problem was that the vacuum motor had a plastic tab allowing it to be mounted only one way. I cut it off to allow me to mount it rotated 180 degrees. It's worked fine ever since.

Thanks for the tip. I tried doing what you said, but for the life of me, I couldn't get the lever in the hole after turning it 180 degrees. I did connect it back the normal way, and so far I haven't had anymore problems. If it falls off again I at least know where the source of the problem is, and I have an alternative. Again, thanks.

I have the exact same problem with my '97 and just logged on to post something. I believe this is probably related to a leaking vacuum line connected to the function selector switch, or perhaps the switch itself is bad. I just discovered this on mine the other day. In addition, when I select "Floor/Panel", the compressor engages, which I don't think it's supposed to do. I'll probably wind up taking mine to the dealer since I don't have time to shade tree this problem. If you find an easy cure please post something.

Good Luck!

I had the same problem with my 1997 Ford F150XL and checked my vacum hose on the cabarator vacum diafram and found no suction. So I knew there was a vacum problem which also was affecting my dash vents by not switching. It took me about 10 minutes doing the complete research and fix. I found the vacum hose connection in behind the battery on the passanger side,....completely disconnected,....which was also afecting my rough idling at start up and check engine light always comming on. I used a tiny bit of dish soap rubbing it on the rubber end connecting hoses to slide them back on 100% and some Duck Tape to hold the pieces back together for good Now everything is working like new again.

[QUOTE=Calguy;5092053]I had the same problem with my 1997 Ford F150XL and checked my vacum hose on the cabarator vacum diafram and found no suction. So I knew there was a vacum problem which also was affecting my dash vents by not switching. It took me about 10 minutes doing the complete research and fix. I found the vacum hose connection in behind the battery on the passanger side,....completely disconnected,....which was also afecting my rough idling at start up and check engine light always comming on. I used a tiny bit of dish soap rubbing it on the rubber end connecting hoses to slide them back on 100% and some Duck Tape to hold the pieces back together for good Now everything is working like new again.